fix(Popover): failed to compile

src/popover/index.js

@@ -1,6 +1,4 @@
-import { createPopper } from '@popperjs/core/lib/popper-lite';
-import offsetModifier from '@popperjs/core/lib/modifiers/offset';
-import extendsHelper from '@babel/runtime/helpers/esm/extends';
+import { createPopper, offsetModifier } from '@vant/popperjs';
 import { createNamespace } from '../utils';
 import { BORDER_BOTTOM } from '../utils/constant';
 
@@ -11,13 +9,6 @@ import { ClickOutsideMixin } from '../mixins/click-outside';
 import Icon from '../icon';
 import Popup from '../popup';
 
-// add Object.assign polyfill for popper.js
-// see: https://popper.js.org/docs/v2/browser-support/
-/* istanbul ignore if */
-if (!Object.assign) {
-  Object.assign = extendsHelper;
-}
-
 const [createComponent, bem] = createNamespace('popover');
 
 export default createComponent({